Prephenate dehydratase from Bacillus subtilis is an excellent example of a regulatory protein under the control of multiple allosteric effectors. The end-product of the biosynthetic pathway, phenylalanine, feedback-inhibits the enzyme, causing it to dissociate to a monomer (55,000 daltons). Tryptophan also inhibits while methionine and leucine activate and induce association to a tetramer (210,000 daltons). The latter three are the end products of other biosynthetic pathways, indicating a complex regulatory pattern. This protein is of relatively low molecular weight, will be available in quantity, and work described in the literature suggests several lines of investigation leading to elucidation of the mechanism by which allosteric transitions are induced and how they regulate activity. We plan to: 1. Develop affinity chromatographic purification procedures involving affinity adsorbents specific for allosteric and active sites; 2. Completely characterized the homogeneous protein by physical and chemical techniques; 3. Use affinity labeling, chemical modification, and changes in environment (pH, temp., etc.) to study allosteric transitions; and 4. Attempt to crystallize the purified protein for crystallographic analysis.